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A P I MPMS*b*b 92 II 0732290 O096227 7 m

Manual of Petroleum Measurement Standards Chapter 6-Metering Assemblies

Section 6-Pipeline Metering Systems

SECOND EDITION, MAY 1991

American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005 rT>

COPYRIGHT American Petroleum InstituteLicensed by Information Handling ServicesCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services

Manual of Petroleum Measurement Standards Chapter 6-Metering Assemblies

Section 6-Pipeline Metering Systems

Measurement Coordination Department SECOND EDITION, MAY 1991

American Petroleum Institute


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SPECIAL NOTES

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Copyright@ 1991 American Petroleum Institute


- A P I MPMS*b-b 91 W 0732290 009b230 7 W

FOREWORD

This publication provides guidelines for selecting the types and sizes of meters for use on pipelines.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Tnstitute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Measure- ment Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

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CONTENTS

Page

SECTION 6-PIPELllW METERING SYSTEMS 6.6.1 Introduction ..................................................... 1 6.6.2 Scope .......................................................... 1 6.6.3 Field of Application .............................................. 1 6.6.4 Referenced Publications ........................................... 1 6.6.5 Meter Station Design .............................................. 1

6.6.5.1 Meter Selection .............................................. 1 6.6.5.1.1 Viscosity .............................................. 2 6.6.5.1.2 Density ............................................... 2 6.6.5.1.3 Corrosive. Abrasive. and Foreign Materials . . . . . . . . . . . . . . . . . . . 2 6.6.5.1.4 VaporPressure ......................................... 2 6.6.5.1.5 Flow Rate ............................................. 2 6.6.5.1.6 Temperature ........................................... 2 6.6.5.1.7 Continuous or Intennittent Service .......................... 3 6.6.5.1.8 Location ............................................... 3

6.6.5.2 Meter Sizing ................................................ 3 6.6.5.2.1 General Considerations ................................... 3 6.6.5.2.2 Sizing Displacement Meters ............................... 3 6.6.5.2.3 Sizing Turbine Meters .................................... 3

6.6.5.3 Instrumentation and Accessories ................................ 4 6.6.5.3.1 Strainers and Filters ..................................... 4 6.6.5.3.2 Water Separators and Water Monitors ....................... 4 6.6.5.3.3 Back-Pressure Valves .................................... 4 6.6.5.3.4 Flow Control Valves ..................................... 4 6.6.5.3.5 AirRemovers .......................................... 4 6.6.5.3.6 Flow Conditioning ...................................... 5 6.6.5.3.7 Displacement Meter Counters ............................. 5 6.6.5.3.8 Turbine Meter Counters .................................. 5 6.6.5.3.9 Ticket Printers ........................................... 5

6.6.5.4 Samp~ng ................................................... 5 6.6.5.5 Proving .................................................... 5

6.6.5.5.1 Tank Provers ........................................... 6 6.6.5.5.2 Conventional Pipe Provers ................................ 6 6.6.5.5.3 Small-Volume Provers ................................... 6 6.6.5.5.4 Master-Meter Provers .................................... 6

6.6.5.6 Typical Pipeline-Meter Station Layouts ........................... 6 6.6.6 Meter Station Operation ........................................... 6 6.6.7 Meter Performance ............................................... 6

6.6.7.1 Net Standard Volumes ........................................ 6 6.6.7.2 Meter Proving ............................................... 9 6.6.7.3 Meter Factor Control Charts .................................... 9

Figures 1-Typical Schematic Arrangement of Pipeline-Meter Station

2-Typical Schematic Arrangement of Pipeline-Meter Station With Three Displacement Meters ..................................... 7

With Two Turbine Meters .......................................... 8

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Chapter 6-Metering Assemblies

SECTION 6-PIPELINE METERING SYSTEMS

6.6.1 Introduction The three principal characteristics of a pipeline that affect

the selection of the type of measurement equipment best suited to it are: a. The high fixed cost, which makes continuous operation desirable. b. The capacity, which implies large volumes and high rates. c. The need for efficient operation and maximum accuracy in measuring the throughput of the system.

The advantages of dynamic measurement (metering) over static measurement (gauging) for pipeline oil movements are provided in Chapter 5.1.

This chapter deals with liquid hydrocarbons (crude oils, condensates, refined products, and hydrocarbon mixtures). Two-phase fluids are not included.

Individuals concerned with installing measurement equipment for liquid hydrocarbons of high vapor pressures, such as ethane-propane mixes, propylenes, and so on, may find this chapter useful; however, special additional precautions may be required.

6.6.2 Scope This chapter provides guidelines for selecting the type and

size of meter(s) to be used to measure pipeline movements. Types of accessories and instruments that may be desirable are specified, and the relative advantages and disadvantages of the methods of proving meters by tank prover, by conventional pipe prover, by small volume prover, and by master meter are discussed. This chapter also includes discussions on obtaining the best operating results from a pipeline-meter station.

6.6.3 Field of Application The information provided in this chapter may be applied

to the following systems: a. Gathering systems from production facilities to a main crude oil storage or pipeline system. b. Crude oil pipelines. c. Refined product pipelines. d. Liquefied petroleum gas (LPG) pipelines.

6.6.4 Referenced Publications Many of the aspects of the metering functions are con-

sidered at length in other parts of this manual. Please refer to the following chapters for more information.

API Manual of Petroleum Measurement Standards

Chapter 4”‘Proving Systems” Chapter 4.3, “Small-Volume Provers” Chapter 5“‘Metering” Chapter 5.1, “General Considerations for Measurement by Meters” Chapter 5.2, “Measurement of Liquid Hydrocarbons by Displacement Meter” Chapter 5.3, “Measurement of Liquid Hydrocarbons by Turbine Meters” Chapter 5.4, “Accessory Equipment for Liq- uid Meters” Chapter 5.5, “Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems” Chapter S-“Sampling” Chapter 12.2, “Calculation of Liquid Petroleum Quantities Measured by Turbine or Displacement Meters” Chapter 13.2, “Statistical Evaluation of Meter Proving Data” (under development)

6.6.5 Meter Station Design

As defined in this publication, a metering station on a pipeline system is one where custody transfer measurement takes place through one or more meters. When a pipeline- metering system is designed, the objective is to obtain optimum measurement accuracy for custody transfers regardless of the volume handled. The measurement accuracy of the system depends on meters, provers, valves, and other equipment selected for that measurement system.

Other considerations for a meter station design include providing for future expansion and upgrades, accessibility of the equipment for maintenance, and accuracy verification.

Chapters 4 and 5 of this manual should be consulted for further requirements common to all proving and metering systems.

6.6.5.1 METER SELECTION

Although displacement meters (see Chapter 5.2) and turbine meters (see Chapter 5.3) are the most commonly used meters in pipeline applications, other types of meters are not excluded if they serve the intended purpose.

Meter selection is discussed in Chapter 5.1. In general, turbine meters are preferred for high-flow rate and low- viscosity applications. In high-pressure applications, capital

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and installation costs of turbine meters may be less. However, in crude oil service viscosity, wax content or the presence of fibrous material may limit the use of turbine meters. When the relative merits of displacement and turbine meters are evaluated, both maintenance and operating costs should be considered. Maintenance costs for displacement meters may be significant when liquids with poor lubricity or abrasive characteristics are handled. Turbine meter maintenance costs are usually low, but maintenance of adequate back-pressure to ensure accuracy may result in higher power costs.

Before selecting a meter, the designer must know or have a good estimate of the following:

a. The range of physical and chemical characteristics of the liquid in:

l. Viscosity, lubricity, and pour-point. 2. Density (API gravity). 3. Corrosive, abrasive, fibrous, wax, or other foreign material. 4. Vapor pressure.

b. The range of flow rates and pressures. c. The range of liquid temperature and ambient temperatures that will be encountered. d. The duration of operation (continuous or intermittent). e. The location of the meter station and whether its control is to be local or remote, attended or unattended.

6.6.5.1 .I Viscosity

The linearity of a displacement meter improves as the viscosity of the fluid being metered increases. This improvement is a result of decreased slippage in the meter. (See Chapter 5.2.)

Turbine meters generally perform with a broader linear range in lower viscosities. (See Chapter 5.3.)

Turbine meters would normally be selected for use with low-viscosity refined products, such as propane, gasoline, diesel oil, and so on, because of their longer service life, greater rangeability, and equal or better accuracy than a displacement meter on these types of products. (See Chapter 5.1.)

6.6.5.1.2 Density

The rating of a displacement meter is generally not affected by the density of the liquid that it must measure. In installations where turbine meters are used, the linear range of the meter tends to shift with density. (See Chapter 5.3.) In general, a turbine meter's normal flow range shifts to a higher range as density decreases. Conversely, for higher density liquids, the pressure drop across the meter increases more rapidly as flow rate increases.

6.6.5.1.3 Corrosive, Abrasive, and Foreign Materials

Abrasive solids, acid or alkaline chemicals, and some salts are typical foreign materials in a petroleum liquid that can harm a meter and its operation. If displacement meters are intended for use with liquids containing relatively large amounts of abrasive or corrosive materials, the manufacturer should be consulted about the materials used for meter construction.

In general, a limited amount of fine abrasives and corrosive contaminants have less effect on the life and performance of a turbine meter because solids in suspension continue to flow uninterrupted through the meter. Corrosive contaminants do not affect, to any marked degree, typical stainless steel turbine meters. On the other hand, displacement meters are more affected by fine abrasives because of the close clearances of the moving parts and because the standard materials of construction can be affected by reactive chemicals. Conversely, fibrous materials, weeds, and wax, which are sometimes present in crude oils, have little effect on displacement meters. However, these contaminants tend to become lodged on rotor blades and straightening sections of turbine meters and affect their operation.

6.6.5.1.4 Vapor Pressure

The vapor pressure of the liquid to be metered is a factor in determining the pressure rating required for the meter and the meter manifold. Vapor pressure also has a bearing on the type of pressure control equipment and valves needed to maintain a liquid phase and accurate measurement.

6.6.5.1.5 Flow Rate

The selected meters shall have the capacity to handle the minimum and maximum expected pipeline flow rate. Dis- placement meters are normally selected for continuous operation at about 75 percent of the manufacturer's nameplate capacity, if the liquid has reasonable lubricity. The capacity of displacement meters is reduced to as low as 40 percent of nameplate capacity for liquids with poor lubricity, such as butane or propane. Turbine meters may be operated at full nameplate capacity and beyond, but because pressure drop increases with flow rate, power costs may be a factor in choosing the most suitable size of meter.

Optimum accuracy may require displacement meters to be operated at rates above 20 percent of maximum nameplate capacity. Turbine meters, depending on fluid characteristics, may require operation at rates above 40 percent of maximum nameplate capacity for optimum accuracy.

6.6.5.1.6 Temperature

When pipelines generally operate in moderate ambient


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SECTION 6"PIPELINE METERING SYSTEMS 3

temperature ranges, special femperature considerations in meter selection or installation are seldom necessary. How- ever, if abnormal temperatures are anticipated, such as high temperatures that may be required for handling high pour- point liquids, consultation with meter manufacturers may be required before meter selection. In addition, handling of hot hydrocarbon liquids may require insulation, heat tracing, or both, of meter manifolding and exposed sections of the tank or lines feeding the meters.

In cold climates, it may be necessary to protect a meter's auxiliary equipment (such as counters and printers) by installing a heated shelter over the meter to prevent failure of the auxiliary equipment. This precaution becomes more critical when electronic equipment is used. Changes in the temperature of a hydrocarbon liquid cause changes in its viscosity. In turn, this change results in a shift of meter factor and a possible shift in normal operating range.

6.6.5.1.7 Continuous or Intermittent Service

Both displacement and turbine meters are designed for either continuous or intermittent service. However, for continuous operation, some arrangement must be provided for standby metering or alternate methods of measurement to cope with normal meter maintenance, scraper runs, or equipment trouble. (See 6.6.5.2.)

6.6.5.1.8 Location

Displacement meters with mechanical registers are well suited to small capacity systems and remote locations. They do not necessarily require uninterrupted electric power and electronic equipment to provide a readout of quantity measured as turbine meters do.

6.6.5.2 METER SIZING

6.6.5.2.1 General Considerations

In new meter stations, the system may be more flexible and less costly if a bank of meters in parallel is installed rather than a single large meter and a single large prover. If an existing prover is to be used, then the new meters selected should be compatible with the existing prover. See Chapter 4 for size limitations of provers.

6.6.5.2.2 Sizing Displacement Meters

If a new measurement system is to be installed, the size of the displacement meters (see Chapter 5.2) may be decided by using the following steps: a. Determine the maximum and minimum meter station flow rates expected. b. If pipeline flow cannot be interrupted, provide a spare meter run so that measurement may continue at the normal

rate if the primary meter fails. c. Size each displacement meter for normal operation at 75 percent of its maximum nameplate capacity.

In most cases when a tank prover is to be used, a minimum of two meters in parallel will be required because flow from the meter to be proved has to be stopped immediately before and after proving. It may not be practical to interrupt the pipeline flow to achieve this requirement except in cases of small lease automatic custody transfer (LACT) gathering systems.

Final selection depends on the performance desired, the space available, and the size and cost (capital and operating) of the meters, prover, associated valves, piping, and auxiliary equipment.

6.6.5.2.3 Sizing Turbine Meters

Sizing a turbine meter requires more detailed considerations than that for a displacement meter because turbine meter performance is more likely to be affected by liquid density and viscosity. (See Chapter 5.3.) Turbine meters tend to be chosen for meter stations that are operated at higherflow rates and lower viscosities.

Fibrous and foreign material tends to get caught on turbine meters in service. It is, therefore, desirable to have a spare meter that can be rotated with the operating meter to allow for disengaging and flushing away fibrous and foreign material before the meter is returned to service. When flow cannot be interrupted, it is desirable to have an alternate meter run so that the contaminated meter can be removed, in- spected, and cleaned. In crude oil service and when permis- sible, it may be desirable to have a back-flushing system that permits reverse flow for a short period to remove material trapped on the turbine blades.

When the size and number of meters needed to meet the required station flow rate are determined, the viscosity and density must be considered. As viscosity increases, the range of flow over which the meter's linearity is acceptable decreases; therefore, greater meter capacity may be required to satisfy a given flow rate. As the density of a liquid decreases, the entire linear portion of the performance curve moves toward the higher flow rates; that is, a liquid with a density of around 0.5 may effectively have the meter over- ranged by a factor of 1.5 times ifs maximum nameplate capacity with no appreciable increase in pressure loss.

Because the performance of turbine meters tends to improve with increased size, caution should be exercised before smaller sizes are selected, especially for crude oil service. Thus, a simple formula to determine the number of meters required for a specific application cannot be given. Manufac- turers should be consulted for particular applications.


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4 CHAPTER 6"METERING ASSEMBLIES

6.6.5.3 INSTRUMENTATION AND ACCESSORIES

Accessory equipment and instrumentation for meters are discussed in Chapter 5.4. Accessories widely used in pipeline meter stations include those described in 6.6.5.3.1 through 6.6.5.3.9.

6.6.5.3.1 Strainers and Filters

Strainers and filters incorporated into pipeline-metering stations should not be used to clean the stream for quality improvement. They should be used only to remove solids that might otherwise damage a meter or create uncertainty of measurement.

Meters can be protected individually or as a bank. With displacement meters, the strainer can be installed immediately upstream from the meter. (See Chapter 5.2.) With turbine meters, the problem of liquid swirl has to be considered. A pipeline-meter station and a filter or strainer should be placed well upstream from the meter run. (See Chapter 5.3.)

Strainers used in crude oil service should be equipped with a coarse basket (usually four mesh is sufficient) to protect the meter-straightening vane and prover from damage by foreign material other than sediment and water. The use of too fine a mesh often defeats the purpose of the strainer because the possible accelerated accumulation of trash may create excessive pressure drop across the strainer. This could lead to rupture of the basket or to vaporization of the liquid. Either of these events affect measurement accuracy. Therefore, it is usually desirable to monitor the pressure differential across a basket with an alarm system or other suitable means.

6.6.5.3.2 Water Separators and Water Monitors

Water separators and water monitors are generally con- fined to uses in crude oil gathering and aircraft fueling systems. Monitors are sometimes used at initiating meter stations of a pipeline when suction is taken from crude oil or jet fuel storage tanks and when it is practical to prevent water from entering the system.

In gathering systems, a water monitor is installedupstream from the meter to suspend shipments to the pipeline automatically if the water content exceeds a pre-set value. This monitor may be used to prevent water from entering the pipeline or its storage system.

6.6.5.3.3 Back-Pressure Valves

A back-pressure valve shall be installed downstream from the meter station if the line resistance downstream is insuffi- cient to maintain pressure on the system consistently high enough to prevent vaporization at all operating conditions. In all systems, adequate back-pressure must be maintained to ensure accurate measurement. For turbine meters, the minimum back-pressure should be approximately twice the pres-

sure drop across the meter at maximum flow rate plus 1.25 times the absolute vapor pressure of the liquid at maximum operating temperature. (See Chapter 5.3.7.3.8.)

These approximate rules vary with the application. For example, turbine meters generally require more back-pressure than an equivalent displacement meter (in nameplate capacity) because of the turbine meter's flowpath, which accelerates the velocity and thus reduces static pressure that can cause vaporization or gas release and subsequent cavita- tion. Although back-pressure is a critical requirement for measurement, excessive back-pressure may result in excessive power costs. A back-pressure valve should be of fail-safe design. It should resist flow as pressure decreases and open as liquid pressure increases. A flow control valve may double as a back-pressure valve when it is placed downstream of the meter.

6.6.5.3.4 Flow Control Valves

If the flow rate needs to be limited through a pipeline- meter station, the manually or automatically operated control valve, should be installed downstream from the meter so that vapor breakout occulTing in the valve does not affect measurement. However, such an arrangement may imply that the pressure in and around the meter manifold would require pressure ratings to be one or more levels higher. In the case of displacement meters, this situation would considerably increase the cost of the meters, filters, strainers, and other accessories used with them. In the case of turbine meters, the added cost for a higher pressure rating may be lower, but the cost of accessories may still be a factor.

If, for reasons of cost, the flow control valve needs to be installed upstream from the meter, installation should be as far upstream as practical. In the case of a turbine meter, installation of the control valve should be at least 50 pipe diameters upstream from the meter. If the action of the control valve causes vapor breakout, the vapor must be removed from the stream before it reaches the meter. Installation of aback- pressure valve downstream from the meter may still be required to maintain pressure on the meter. (See 6.6.5.3.3.)

6.6.5.3.5 Air Removers

Air removers (air eliminators) should be installed upstream from the meter if air or vapors might enter the metered stream and adversely affect measurement. However, in most installations, the entrance of air may be more practi- cally prevented by automatic air-sensing shut-off systems than by removing the air once it has entered the flowing stream. This is particularly true of crude oil service. Air removers operate by reducting stream velocity through

an expansion of cross section. This principle allows entrained lighter gases to escape upwards if the viscosity of the liquid is not too great to delay or halt the process. A series of baffles


SECTION 6-PIPELINE METERING SYSTEMS -

assists in the separation. As air, gas, or vapor accumulates, a float valve opens and allows escape.

In a pipeline-meter station, if a high vacuum (negative head) could possibly exist, a check valve should be installed in vent lines to prevent air being drawn into the air remover. It is also advisable in pipeline-meter stations to install one or more vent valves at high points in the station manifolding. This precaution allows the air to be bled off after maintenance or drain-downs.

6.6.5.3.6 Flow Conditioning

Pipeline-meter stations that use turbine meters shall have a flow-conditioning section installed upstream and a recovery section installed downstream of each meter. See Chapter 5.3 for a full description of the arrangement and the details of the effect of piping configurations on swirl. Flow conditioning is not usually required in installations where displacement meters are used.

6.6.5.3.7 Displacement Meter Counters

Frequently, a small-numeral, mechanical, non-resettable totalizer counter that registers in whole, appropriate units is used on displacement meters to indicate metered throughput. In addition to the non-resettable totalizer, a mechanical, resettable, large-numeral counter that registers in fractions of a unit (that is, a cubic meter or barrel) for use whenproving into tank-type provers may beincluded on the meter. Thesmallest fractional increment to be displayed on the large-numeral counter depends on the size of prover used.

Large-numeral, resettable counters may be used wherever they offer an advantage, provided that indicated volumes of oil measured are read from the non-resettable counter. Large- numeral counters may be fitted with a monitor switch that can be used to pulse a remote register or to detect meter failure. This switch should be operated by the non-resettable counter. This feature can be valuable at unattended stations.

A high-resolution pulse transmitter and high-resolution proving counter are required when proving a displacement meter with a pipe prover. (See Chapter 4 for details.)

6.6.5.3.8 Turbine Meter Counters

Turbine meters generally are connected to one non- resettable totalizer counter that reads in whole units per meter and that indicates the metered throughput. Additional counters, such as prover or net counters, may be added as the need arises without affecting meter performance. A discrete high-resolution pulse-proving counter that is gated by the prover’s detector switches is required for proving a turbine meter. (See Chapter 5.4 for information on counters and Chapter 5.5 for information on electronic pulse transmission systems.)

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6.6.5.3.9 Ticket Printers

Ticket printers are discussed in detail in Chapter 5.4. Mechanical and electrical printers are the two most common types.

Mechanical printers are generally used with displacement meters because they can be coupled directly to the meter’s output shaft and do not require an external power source. A mechanical printer can also be used with a turbine meter, but in this arrangement, pulses generated by the meter drive a stepper motor which, in turn, drives the register and printer. (See Chapter 5.4.)

Electrical or electrical-mechanical printers can be used with either type of meter, but they require an electric signal, generated by the meter, to be electrically coupled to the printer. Electrical printers are generally suited to turbine meters which directly generate electric signals. They are also used for totalizing a number of meters or for remote readout. Although an external power source is required, electrical printers have the advantage of minimizing torque on the meter output. (See Chapter 5.4 for a further description.) Dual registers and printers can be used to facilitate swings from batch to batch either manually or automatically. Multiple meter-pulse combinators, temperature-compensating equipment, and similar devices are discussed in Chapter 5.4. Spe- cial attention must be given to the installation of electronic systems to ensure that extraneous pulses are not registered. Shielded conductors, proper grounding of equipment, and shielding are essential. (See Chapter 5.5.)

6.6.5.4 SAMPLING

Because pipeline movements are measured in batches or tenders that may differ appreciably in liquid properties (viscosity and density), the stream interfaces must be sampled to segregate batches for meter proving and to assign meter factors to be applied to each batch. Other aspects of sampling (for example, determining crude oil quality) that require representative samples be taken by proportional sampling techniques are discussed in Chapter 8.

6.6.5.5 PROVING

A pipeline-meter station shall have either a fixed prover, connections for a portable prover, or master-meter proving. Chapter 4 should be consulted before the proving arrange- ments for a station are designed. The four standard methods of proving by conventional pipe prover, small-volume prover, tank prover, or master-meter prover are described in Chapter 4. See Chapter 12.2 for an explanation of the standard methods of calculating petroleum quantities and determining meter factors. The decisions reached as a result of design deliberations in 6.6.5.1 and 6.6.5.2 will largely determine the selection of the most suitable meter-proving systems.


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6.6.5.5.1 Tank Provers

Tank provers have a capital cost advantage over pipe provers in fixed installations. In small-capacity or remote pipeline-meter locations without electric power, tank provers can be used for accurate proving of displacement meters. The tank prover is not readily adapted to automation or remote control. Tank provers have the disadvantage of requiring two or three tank fillings per meter proof, which have to be returned to a line under pressure. Reproducible drainage of prover tank walls is also critical. This feature is a further disadvantage of tank provers over pipe provers and master meters.

Tank provers are not suitable for high-vapor pressure products because the product may be lost by evaporation from an open-tank prover during the prover operation. Tank provers may not be suitable for viscous liquids that may not completely drain from the inner surfaces of the tank prover during drain-down between proving runs.

6.6.5.5.2 Conventional Pipe Provers

Conventional pipe provers are readily adapted to automation and remote control and are capable of fast, easy, and reproducible proving in either a fixed or portable arsange- ment. Conventional pipe provers are relatively expensive, but if used by a number of small stations in the portable or mobile mode, their capital cost can be disbursed accordingly. In most large or new stations, conventional pipe provers have advantages over other methods.

A portable pipe prover can be equipped with its own power supply, making it usable at a meter station where power is not available.

6.6.5.5.3 Small-Volume Provers

Small-volume provers share the advantages of conventional pipe provers and, being small, are well adapted to portable applications. (See Chapter 4.3 for details.)

6.6.5.5.4 Master-Meter Provers

Master-meter proving is used when other prover methods are not practical. It is sometimes used as a backup to the other proving systems, and with small changes to the station manifold, it can be applied to any existing station. A master meter can be used in conjunction with a mobile pipe or tank prover to prove operating meters at any station.

6.6.5.6 TYPICAL PIPELINE-METER STATION LAYOUTS

Figure 1 shows a schematic diagram of a typical displacement meter installation. Figure 2 shows a typical turbine meter installation. The expected measurement conditions of each installation dictate what options are necessary; not all

options shown in the schematics may be required, and options not shown may still be required.

6.6.6 Meter Station Operation This publication is intended to assist the designer of a

pipeline-meter station to select and install the equipment appropriate to the needs of its proposed operation. Chapters 4 and 5 contain much information that applies to pipeline- meter station design, selection, and installation, and these chapters also contain most of the information affecting their operation and maintenance.

The operator of a pipeline-meter station, therefore, know- ing the type of liquids involved, the type and size of meters and proving systems provided, and the range of values of the principal variable-rate, viscosity, temperature pressure, and density-should review those parts of Chapter 5 that deal with meter pesformance, operation, and maintenance, bearing in mind the considerations described in 6.6.7.

6.6.7 Meter Performance Meter performance is a general expression and is used to

indicate how satisfactorily a meter can continuously measure the actual volume of liquid passing through it. It is most often shown as a characteristic os performance cume, which is a plot of meter factor versus rate. Because a meter factor is applied to the indicated volume in all pipeline-metering systems involving liquid hydrocarbons, the usefulness of the characteristic curve lies in its ability to show by how much a meter factor will change with a given change in rate. In- dividual curves should be made for each product or grade of crude oil.

Meter performance can also be plotted as meter factos versus any operating parameter, that is, viscosity, temperature, and so forth. However, when the liquid properties change significantly (for example, when a new batch or tender is to be measured), a new meter factor should be developed by re-proving. The most common presentation of meter performance is a plot of meter factor versus rate at stable operating conditions. Meter proving should be done frequently if maximum accuracy is essential.

6.6.7.1 NET STANDARD VOLUMES

The custody transfer measurement of hydrocarbon liquids is performed to obtain a quantity definition that is the basis for commercial transactions. This quantity is most often expressed as a net standard volume. Net standard volumes ase volumes corrected for meter factor, for the effects of temperature and pressure on both the liquid and the steel of the prover used to determine the meter factor, and for sediment and water content, if applicable.

The standard methods for calculating a prover's base volume, a meter factor, and a measurement ticket are detailed


A P I MPMS*b-b 91 m 0732290 0096238 I m

SECTION &PIPELINE METERING SYSTEMS 7

Mainhe

To storage I

Q 4 5

10 / is;1 I 2 4'

H 4

10 / Is;1 2

1 i1 4

n 5 4 J

i1 4

10 / H 10 Q I /

2

see Chapter 4

v 8' To prover I

i 10

From prover F

1. Pressure-reducing valve-manual or automatic, 6. Check valve, if required. if required. 7. Control valve, if required.

2. Filter, strainer and/or vapor eliminator 8. Positive shut-off, double block and bleed valves. (i required) for each meter or whole station. 9. Flow control valve, if required.

3. Displacement meter. IO. Block valve, if required. 4. Temperature measurement device. 11. Differential pressure device, if required. 5. Pressure measurement device. 12. Sampler, proportional to flow.

Note: This simplified diagram indicates primary components for typical stations but is not intended to indicate preferred locations. All sections of the line that may be blocked between valves should have provisions for pres-

I sure relief (preferably not to be installed between the meter and the prover).

Figure I-Typical Schematic Arrangement of Pipeline-Meter Station With Three Displacement Meters


8

A P I MPMS*beb 91 I 0732290 0096239 3 I

CHAPTER &METERING ASSEMBLIES

a

2

< 6 D

4 ío diameters

5

5

W diameters

1 To storage

ío a 7

b

í2 D(

I í

7 I

1 /

[5;1 í i

3

-g f W Flow

ío

1

see I To prover 4-

Chapter 4 1 From prover 1 F

Mainline

1. Block valve, if required. 2. Differential pressure device, if required. 3. Filter, strainer andor vapor eliminator

4. Stralghtener assembly. 5. Turbine meter. 6. Meter run (straight pipe).

(if required) for each meter or whole station.

7. Pressure measurement device. 8. Temperature measurement device. 9. Positive shut-off, double block and bleed valve.

I O . Control valve, if required. 11. Check valve, if required. 12. Sampler, proportional to flow.

Il

Note: This simplified diagram indicates primary components for typical stations but is not intended to indicate preferred locations. All sections of the line that may be blocked between valves should have provisions for pressure relief (preferably not to be installed between the meter and the prover).

Figure 2-Typical Schematic Arrangement of Pipeline-Meter Station With Two Turbine Meters


A P I MPflS*b.b 71 m 0732290 007b240 T m

SECTION &PIPELINE METERING SYSTEMS 9

in Chapter 12.2. The derivation and calculation of all the correction factors that enter therein are also described in Chapter 12.2. Standard conditions to which most volumes are corrected are 60°F and 14.73 pound per square inch absolute.

6.6.7.2 METER PROVING

Refer to Chapters 4 and 5 for general guidelines on meter proving.

In a pipeline-metering system, additional consideration should be given to proving the meters each time there is a change of product through the metering assembly. Other considerations may include changes in flow rate, temperature, or pressure that may cause a measurable change in meter factor.

6.6.7.3 METER FACTOR CONTROL CHARTS

Another way of plotting a meter’s performance is by keeping a meter factor control chart for each product or grade of crude oil. (See interim Chapter 13.2.) Such a control chart is essentially a plot of meter factor versus time, that is, a graphical record of meter factor values over months or years. Because control charts show valid limits for random distribu- tion of meter factor values, they can be used as an aid in judging the correct frequency of proving and the acceptable repeatability of values during a proof and also in deciding when inspection or maintenance is needed.

A log book of preventive and repair maintenance should be kept at each meter station for each meter so that costs and performance can be compared from time to time. A notation on the control charts should also be made.


A P I MPMS*b-b 91 I 0732290 0 0 9 b 2 4 1 L m

Order No. 852-301 26


A P I MPMS*b.6 91 0732290 0096242 3

American Petroleum Institute 1220 L Street, Northwest


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